1. Field of the Invention
This invention relates polymer chemistry used to formulate coatings
2. Introduction
Polymer resins serve an important niche in structural engineering by offering the engineer the ability to tune the tensile strength, hardness, corrosion resistance, deformability and optical properties on a continuum scale by merely adjusting the components of the polymerization process. Although polymer resins offer a wide continuum of physical properties, it is virtually impossible a priori to predict a set of physical properties based on a set of initial reactants. One of the more common methods of formulating polymer resins employs mixing a polyisocyanate with either a poly-ol and/or poly-aspartic ester. See e.g. U.S. Pat. Nos. 5,126,170 and 5,236,741. There are a number of advantages with formulating polymer resins in this manner. These formulations are simple, cost effective, and by varying either the ratio of the polyisocyanate and the aspartic ester/poly-ol or by varying the kinds of polyisocyanate and aspartic ester/poly-ol employed, a wide range of the polymers with different physical properties can be produced. There are however, some significant disadvantages with these formulations. Polymer formulations based on polyisocyanate and poly-aspartic ester mixtures tend to deteriorate over time leading to coating softening and ultimately delamination. Coating failure is further accelerated when a coating is exposed to moisture or applied in layers greater than 20 millimeters. Although the exact mechanism of the failure of polyisocyanate/poly-aspartic ester based polymers is unknown, it is believed a rearrangement reaction occurs releasing ethanol which then accumulates in the coating causing coating failure.
In addition to forming coating polymers from polymeric addition reactions between polyisocyanates and poly-aspartic esters, coating polymers may also be formed from addition reactions between polyisocyanates and cycloaliphatic amines. See e.g. U.S. Pat. No. 5,312,886. This latter class of polymers, although offering improved physical characteristics compared to the poly-aspartic based polymers, is very expensive to manufacture due to the high price of cycloaliphatic amines. Sterically hindered cycloaliphatic amines cost approximately three times the cost of poly-aspartic amines.
Accordingly, a coating composition is needed that resists softening with time, is stable in a moist environment, but is still simple and inexpensive to fabricate and allows the physical properties of the polymer resins to be adjusted by adjusting the type and ratios of the polyisocyanates and the polyisocyanate reactive components.
The present invention is based upon the unexpected discovery that if a polyisocyanate is reacted with a polyaspartic ester and a cycloaliphatic amine the resulting polymer resin has superior physical characteristics, including superior hardness, superior resistance to hydrolytic degradation, superior resistance to acid/base catalyzed hydrolytic degradation and superior resistance to melting than resins formed from the mixing of polyisocyanate with either a polyaspartic ester or a cycloaliphatic amine.